The various embodiments described herein generally relate to implantable leads, and more particularly to implantable leads used for measuring pressure of fluids or tissues within a patient's body.
Pressure tracking of fluids or tissue within a patient's body is useful for predicting pathological conditions of the patient. For example, coronary pressure tracking of the blood within the heart and/or the heart tissue is useful for predicting heart diseases that may lead to heart failure. Several types of pressure sensors, used in connection with an implantable medical device (IMD), have been used to measure coronary pressure.
One known type of pressure sensor utilizes strain gauges to measure pressure. These known sensors include wires that are adhered to a surface of the heart. An electrical potential is maintained across the wires and a change in resistance of the wires is measured. The change in resistance correlates to an amount of extension of the wires and translates to the forces acting on the surface, because the amount of extension is based on an amount of deflection of the surface. However, a major drawback to using strain gauges to measure coronary pressure is that the strain gauge requires that an electrical potential be maintained across the wires, which consumes battery life of the IMD.
Another known type of pressure sensor utilizes a piezoelectric sensor to measure pressure. Some known piezoelectric sensors include a piezoelectric strip located at a bend of a J-shaped pacing lead that is implantable in the atrium or ventricle. The piezoelectric strip extends longitudinally along the lead and measures movement of the lead at the bend. Other known piezoelectric sensors include piezoelectric strips that are disposed on a surface of a patch electrode that is adhered to an outer surface of the heart. The piezoelectric sensor measures expansion and contraction of the heart surface. However, one drawback to using the piezoelectric strip to measure coronary pressure occurs because the piezoelectric sensors detect many different forces at the same time, such as lateral forces, shear forces, bending forces and rotational forces. Because many different forces are simultaneously detected, the voltage transmitted by the piezoelectric sensor may be inaccurate. Another drawback to using the piezoelectric strips to measure coronary pressure is that the voltage generated by the piezoelectric sensor typically have a very low signal to noise ratio. One way in which known piezoelectric sensors overcome this problem is to increase the surface area of the piezoelectric strip, thus increasing the overall size of the IMD.